Hello I am thinking about purchasing an 07 5.9L and the truck has 37" tires with 3.73 gears. Is this gear set up okay for 37 " tires or am I going to have problems down the road with this set up?

What will 37" tires and 3.73 gears do to my gas mileage?

What will it do to my speedometer?

Any input would be greatly appreciated

 

You'll have about a 3:15 ratio with the 37's sort of like your grandmother's crown vic. Big tires like that are gonna make it thirsty no way around that. Probably not gonna be much fun towing especially if you don't turn it up with a programmer. Daily driver is probably ok without a gear swap. Google tire, rear ratio, speedometer etc to find calculators.

 

Don't expect the trans. to last too long.

 

what if I drop the tires down to 35's? and if i do not tow anything, I'm i still going to damage the transmission?

 

Big tires doesn't necessarily damage a tranny, abuse does. you didn't say if its an auto or a 6 speed.

With a 6, the 37's will put you about 1800 RPM at 70 MPH, about perfect for cruising. Towing in high gear without your torque converter locked up would kill the tranny. If you tow, just get used to not using overdrive. 5th gear would be 2200 RPM at 65 MPH. The auto shouldn't be far from these numbers for drive and overdrive

Good luck.

Cya

 

thanks for the great info CYA, but the truck I am looking at is an auto. can you please give me the same info in the auto as you did the 6 speed. you say far from these numbers can you explain. thanks

 

At 60 MPH with 37s.

Your speedo will read 60 you will be doing 74 MPH and you will be at 1595 RPM in 6th gear on 2007 G-56 (manual). I cannot tell you a specific amount of fuel mileage you will lose, but you don't see a Camry Hybrid swinging 37s for a reason. You can run 37s with a 4.5 inch lift, but I always thought they look right with a 6 inch lift, personal preference.

 

With my G56 it is right at 1,800RPM @ 65MPH while it used to be turning at 2,200 at the same speed. I used my Smarty with GPS to dial the speedo. At 65MPH highway, I get about 19MPG...not bad. However with the bigger tires, you WILL notice your truck does not stop as fast as it used to...just step on the brake sooner and don't tailgate.

 

Billie - What Rpm Does Your Truck Do At 75 And 80 Mph - I've Got 4:10 And Am Thinking Of Droping To 3:73. I Have Stock Tires - 05 Dodge

 

pro nra, thanks for the input but it sounds like you have the manuel. what can I expect with the auto? should i change my gears to 4:56's?

anyone running 37's with the auto transmission?

 

I'm not sure about the auto as the OD on the auto is taller so I would think it slows it down a bit more than the G56s which is way too short OD hence I went with the 37 to lower the RPM at highway speed since I never tow anything. When I dialed my speedo with the the GPS and Smarty, I had to do several runs as the 37" tires realy is not a 37 to get the speedo right. I had to dial the Smarty right at 35.62.

 

I have 3:73's and 37s and a auto.

I had them recalibrate the speedo...its still off. I have to look at my gps to see how fast Im going.

It does have a noticeable lag, mostly on take off. But it doesnt bug me much. And if it does anything to my tranny...my dealership has already said they will fix it. They sell lifted trucks and built one exact same set up as mine. 3:73's, 37's etc. So Im good...

But I am doing some tranny mods as soon as I can part with my truck and putting in 4:56's to handle 38-40's

 

Hey Erk1974: I have 4:10 and stock tires as well. At 60-61 are you about 1800rpm? Thats what I am seeing. I like how I can charge up a hill with my Outback TT, but it seems 2000plus rpm everywhere else. 65mph is 2100 or more.
so I have been thinking up-sizing the tires a little.
So if I go up to 285/70-17 what is that equalvalent to? 33 or 34 inches tall?
That won't hurt it on take off very much will it?

 

I have an '07 5.9 with 3.73's and 35's. I get a whole 12.25 miles per gallon. Motor, trans, etc COMPLETELY stock. Ha! Not used to that

Before the 35's I got 13-15 depending on driving. Best of 16.1. I don't think you'd be too far off from my current mileage. I'm sure if I drove in town more I'd be in the 11's.

Not bad though. I was at a Ford dealer yesterday picking up my flatbed, and the svc. manager told me I'd be lucky to see 8-9 mpg in the new 6.4!!!

 

Sea Buiscuit - That Sounds About Right - My Truck Pulls Great At 65 To 70 Running About 2000rpm - Id Like To See What Would Happen With A 373 At 2000 Rpm - Maybe Would Tow At 70 - 75. I Would However Want To See What The Fuel Economy Would Do. I Wonder If It Would Go Up For Regular Driving With 373.
For Towing I Might Have To Grab 5th Gear At 60-65 With 373.
Since Now I Tow In 6th At 65 -70 With 410. That Might Be A Reason To Stay With 410 For Me Anyhow. Does Anyone Have Info?